Endothelial and hematopoietic cells are ideal targets for gene therapy because are readily accessible to gene therapy vectors via the circulation and play a critical role in the progression of disease processes including inflammation and tumor angiogenesis. Adenoviral (Ad) vectors which could infect quiescent vascular cells provide ideal vectors to introduce genes into vascular endothelium as well as hematopoietic stem and progenitor cells with high efficiency and low toxicity. However, expression of genes by Ad vectors has been hampered by infiltration of inflammatory cells and intravascular activation of neo-intimal cells. Despite numerous studies defining the role of immune response to Ad vectors the exact mechanism whereby Ad vectors modulate activation status of ECs and hematopoietic cells and subsequent inflammatory response is not know. We have shown that introduction of E1-E4+, but not E1-E4-Ad vectors into primary ECs results in profound alteration in the proliferation and inflammatory status of the ECs. Infection of ECs with E4+ Ad vectors result in the generation of unique state where ECs do not proliferate or undergo apoptosis. This state is also associated with the upregulation of inflammatory adhesion molecules including ICAM, VCAM, and CD34. Moreover, E4 mediated activation of ECs enhance transendothelial migration of hematopoietic precursor cells and proinflammatory cells. These data clearly demonstrate that one or a combination of E4 gene products encoded by seven distinct E4 open reading frames (ORFs) regions may play a critical role in modulation of angiogenic and inflammatory potential of ECs. Based on these data, we hypothesize that gene products encoded by the E4 region of Ad vectors pirate the molecular machinery of ECs resulting in transformation of ECs into a unique pro-angiogenic and proinflammatory state. Identification of E4ORF genes that modulate angiogenic and inflammatory potential of ECs hematopoietic cells will facilitate designing strategies to attenuate vascular toxicity associated with Ad vector gene therapy. The mechanism by which E4ORFs gene products modulate angiogenic and inflammatory potential will be investigated through studying the following experiments: 1) Identifying specific E4ORF genes that alone or in combination modulate angiogenic and inflammatory potential of ECs in in vitro and in vivo models. 2) Assess the effect of E4ORFs gene products in the modulation of angiogenic potential of circulating VEGFR2+AC133+endothelial precursor cells (EPCs) and hematopoietic stem and progenitor cells. 3) Define the mechanism(s) whereby E4ORFs modulate the motility and mitogenic potential of ECs and hematopoietic progenitor and stem cells. 4) Define the role of E4ORFs in physiological models of angiogenesis and inflammation. These experiments may culminate in identification of E4ORFs that promote or inhibit angiogenesis, and diminish E4 mediated vascular toxicity. Incorporation of pro-angiogenic E4ORFs in conjunction with transgenes expressing VEGF, will facilitate developing clinical strategies to enhance collateral formation in ischemic myocardium or limbs. Conversely, E4ORFs with anti-angiogeni properties may be used in clinical strategies that are targeted at inhibiting tumor angiogenesis or blocking aberrant angiogenesis in clinical scenarios, such as diabetic retinopathy.